The present invention relates to a compression ignition internal combustion engine, and more particularly, to a compression ignition internal combustion engine capable of switching a compression ignition combustion and a spark ignition combustion.
As described in JP-A-10-56413, a compression ignition internal combustion engine adopts a combustion system of compressing and self-igniting a uniformly premixed fuel-air mixture. The compression ignition internal combustion engine can operate in an ultra-lean area (air-fuel ratio of 80 or more) that cannot be operated by a conventional gasoline engine or diesel engine, and decreases flame temperatures and realizes ignition combustion with a uniform fuel-air mixture, and therefore it is an engine that allows drastic reduction of both NOx and soot.
Generally, when a fuel-air premixture is compressed and reached at a certain temperature, a reaction called xe2x80x9clow temperature oxidation reactionxe2x80x9d whose initial reaction is dehydrogenation of hydrocarbon as a fuel, starts. When this reaction progresses, an elementary reaction called xe2x80x9cblue flamexe2x80x9d takes place, which leads to self-ignition. Since this ignition takes place at multiple points in the fuel-air mixture simultaneously, the combustion period for the combustion chamber as a whole is by far shorter than combustion by spark ignition of a conventional gasoline engine or a combustion period of injection combustion of a diesel engine. For this reason, this results in a reduction of flame temperature and suppression of NOx generation which is dependent on a duration thereof, which constitutes a factor of realizing low NOx in the compression ignition internal combustion engine.
However, the conventional compression ignition internal combustion engine has a problem that its output torque range is limited to a very narrow range and an engine operation with compression ignition is only realized within quite a limited range of low-load and low-speed rotation. The reason is that the temperature for a fuel-air premixture using hydrocarbon as a fuel to reach self-ignition is said to be 900K or higher and a current gasoline engine whose compression ratio is set to about 10 to 13 is known to have almost no operating area where self-ignition can take place.
Furthermore, the compression ratio can be set as high as that of a diesel engine (16 to 22) and there can be an engine operating area by self-ignition of a fuel-air premixture, but since it is difficult for the conventional engine to control self-ignition timings of the mixture, a combustion period is short and compression self-ignition of the premixture is strongly affected by an air-fuel ratio, etc., its output torque range is limited to a very narrow range, causing a problem that an engine operation by compression ignition can be realized only in quite a limited area of low-load and low-speed rotation.
In contrast, as described, for example, in JP-A-11-280507, an engine is known which flows backward a high-temperature burnt gas (internal EGR) generated in a previous cycle to a combustion chamber by operating a mechanism that makes variable valve timings of intake/exhaust valves, keeps the inside of the combustion chamber at a high temperature through the internal EGR in a low-load area and realizes an operating area by the self-ignition combustion through control over the amount of the internal EGR and real compression ratio and operates by the spark ignition combustion in a high-load area, area.
However, the internal combustion engine described in JP-A-11-280507: has the following problems. That is, the conventional internal combustion engine overlaps the opening periods of intake/exhaust valves to introduce the internal EGR, which causes an amount of the internal EGR to be controlled by the overlapping period of the intake/exhaust valves. The conventional internal combustion engine also controls the intake valve to control ignition timing at the same time. That is, when the opening/closing timings required for the intake valve and exhaust valve vary depending on the engine operating condition, both timings cannot be controlled independently of each other, which causes a problem that the operating area by self-ignition is narrowed.
Furthermore, the conventional engine system that combines the self-ignition combustion and the spark ignition combustion cannot control valve timings and valve lifts of the intake/exhaust valves and the amount of intake air independently of one another when switching a combustion state from the self-ignition combustion to the spark ignition combustion or from the spark ignition combustion to the self-ignition combustion, producing differences in torque causing a problem of making stable driving of a vehicle difficult.
It is an object of the present invention to provide a compression ignition internal combustion engine capable of making compatible an increase in compression self-ignition operating area with an optimum output torque control in the operating area and also smoothly switching between a self-ignition combustion and a spark ignition combustion.
To attain the above object, the present invention provides a compression ignition internal combustion engine for operating by switching a spark ignition combustion using an ignition device and a compression ignition combustion for self-igniting a fuel-air mixture by piston compression, provided with variable valve mechanisms for varying at least one of valve timings and valve lifts of an intake valve and an exhaust valve, intake air regulating means for varying an amount of air intake into a combustion chamber on an upstream side of a combustion chamber inlet of the compression ignition internal combustion engine and control means for controlling the variable valve mechanisms and the intake air regulating means during a compression ignition combustion so as to perform a compression ignition combustion.
Such a configuration makes compatible an increase in the compression self-ignition operating area with an optimum output torque control in this operating area and also allows for smooth switching the self-ignition combustion and the spark ignition combustion.